The invention is a threaded fastener having means for visually indicating whether the fastener is tightened to a predetermined minimum torque.
In many mechanical devices, components are joined together by bolts or other threaded fasteners. Commonly it happens that these devices are subjected to mechanical and thermal stresses tending to separate the components, whereby the fasteners are strained sufficiently to lose tightness of grip. In these instances, the fasteners must be retorqued. Additionally, these fasteners often need to be periodically checked for proper torque to tightness.
In some applications, such as vehicle engine assemblies, transmissions, body structural elements, or suspension elements, the fasteners may be in relatively inaccessible locations. Often the fastener to be checked can not be reached by a torque wrench without substantial disassembly of the vehicle or its components. In some designs, therefore, space around the fasteners is purposely left open or free in order to facilitate access to these fasteners for torque testing. Such designs are not desirable for all vehicle applications, since space is often at a premium in vehicles.
In combat vehicles, for example, space for components is at a premium because the vehicle should have the smallest possible profile exposed to enemy fire. For armored vehicles, every extra cubic foot of vehicle space needs extra square area of armor, and hence more vehicle weight. Excess weight on armored vehicles, some of which weigh 60 tons already, causes a number of problems. These problems include inability to traverse over certain terrains or soils, reduced capacity to carry fuel and ammunition, reduced operating range, and reduced life of suspension and tank track components. Consequently, it is not generally practical to provide access space for fasteners for major components of armored vehicles.
Partial disassembly of armored vehicles to gain access to fasteners has disadvantages as well. Modern armored vehicles are quite complex, so that disassembly and reassembly is difficult and time consuming, especially since removal and replacement of armor plating may be necessary. Also, since armored vehicles are extremely heavy and of unique design, there are relatively few repair depots whose personnel and equipment can undertake disassembly or reassembly of such vehicles.
Applicant's invention is a fastener assembly designed to alleviate the difficulties associated with the need to test the torque or tightness of threaded fasteners on components in armored vehicles. The invention is a means to provide visual indication when the axial clamping force of a bolt or like fastener is above a given threshold, so the fasteners can be tested even when they are inaccessible to torque wrenches. The visual indication means can be configured to permit measurement of the clamping force and to prevent overtorquing of the fastener.